a−b+c. a+2b−c. 5a−7b+1. 5a−7b−1. z+x−y. z−x+y. a−2b+c. x+3y+z. x+3y−z. a+2b+2c. a+2b−2c. 1−3x+2y. [2]Ejercicio29. 1+x+x2. 1+2a+4a2. 1+3c+9c2. 4a2+2ab+b2. 16b2+12bc+9c2. 9x2+6xy+4y2. x2y2+xyz+z2. a2b2+2ab+4. 25a2+5ab+b2. a2+2ab+4b2. a2+4a+16. a6+3a3+9. a8+a4x2y2+x4y4.